Homopolymers of L-alanine, L-arginine, L-histidine, L-lysine, and L-proline and the mixed polymer of L-lysine and L-phenylalanine have been oxidized in the presence of ferrous iron and a chelator, generally citrate. Oxidation introduces carbonyl groups into the polymer which may be converted into secondary amines by reacting them with p-aminobenzoic acid in the presence of sodium cyanoborohydride. Polymers thus derivatized exhibit characteristic spectra which may be measured. The polymers are also cleaved by the oxidation; poly-L-histidine appears to be especially vulnerable to this sort of attack. The greatest rate of oxidation is found when the ratio of ferrous iron to citrate is 1:2.